Sensing a phase-path current in a multiphase power supply such as a coupled-inductor power supply

ABSTRACT

An embodiment of a power supply includes a supply output node, phase paths, and sensor circuits. The supply output node is operable to carry a regulated output voltage, and each phase path has a respective phase-path non-output node, has a respective phase-path output node coupled to the supply output node, and is operable to carry a respective phase current. And each sensor circuit has a respective sensor node coupled to the phase-path non-output nodes and is operable to generate a respective sense signal that represents the phase current flowing through a respective one of the phase paths. For example, where the phase paths are magnetically coupled to one another, the sensor circuits take into account the portions of the phase currents induced by the magnetic couplings to generate sense signals that more accurately represent the phase currents as compared to conventional sensor circuits.

CLAIM OF PRIORITY

This application claims priority to U.S. Provisional Application Ser. No. 60/964,792 filed on Aug. 14, 2007 and U.S. Provisional Application Ser. No. 61/072,287 filed on Mar. 27, 2008, which are incorporated by reference.

SUMMARY

An embodiment of a power supply includes a supply output node, phase paths, and sensor circuits. The supply output node is operable to provide a regulated output voltage, and each phase path has a respective phase-path non-output node, has a respective phase-path output node coupled to the supply output node, and is operable to carry a respective phase-path current. And each sensor circuit has a respective sensor node coupled to the phase-path non-output nodes and is operable to generate a respective sense signal that represents the phase current flowing through a respective one of the phase paths.

For example, where the phase paths are magnetically coupled to one another (e.g., the phase paths include magnetically coupled windings), the sensor circuits are able to account for the portions of the phase currents induced by the magnetic couplings between phase paths, and this accounting allows the sensor circuits to generate sense signals that more accurately represent the phase currents as compared to conventional sensor circuits. The sense signals may be fed back to the power-supply controller, which regulates the output voltage at least partly in response to the fed-back sense signals.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an embodiment of a coupled-inductor multiphase power supply that includes sense circuits for sensing the phase currents.

FIG. 2 is a schematic diagram of a portion of the power supply of FIG. 1 including the phase-path windings, and an embodiment of the sensor circuits of FIG. 1.

FIG. 3 is a schematic diagram of a two-phase version of the power-supply portion of FIG. 2.

FIGS. 4A and 4C are timing diagrams of sense signals that are generated by the sensor circuits of FIG. 3.

FIGS. 4B and 4D are timing diagrams of the phase currents flowing through the windings of FIG. 3.

FIG. 5 is a schematic diagram of a portion of a two phase version of the powers supply of FIG. 1 including the phase-path windings and another embodiment of the sensor circuits of FIG. 1.

FIG. 6 is a block diagram of an embodiment of a computer system having a power supply that includes sensor circuits that are the same as or similar to one or more of the embodiments discussed above in conjunction with FIGS. 2-3 and 5.

DETAILED DESCRIPTION

FIG. 1 is a schematic diagram of an embodiment of a coupled-inductor (CI) multiphase power supply 10, here a CI buck converter, which provides a regulated output voltage V_(out) at a supply output node 11, and which includes phase paths (alternatively “phases”) 12 ₁-12 _(n) and current sensors 14 ₁-14 _(n) for respectively sensing the currents i₁-i_(n) through the phases. As discussed below in conjunction with FIGS. 2-5, the current sensors 14 ₁-14 _(n) may each be coupled to respective multiple phase paths 12 ₁-12 _(n) at nodes or locations other than the supply output node 11. For example, assume that some or all of the phases 12 ₁-12 _(n) are magnetically coupled to one another. Coupling a current sensor 14 not only to a first phase 12 for which the sensor measures the phase current, but also to one or more second phases 12 to which the first phase is magnetically coupled, may allow the sensor to sense the current through the first phase more accurately than some conventional current sensors can.

The current sensors 14 ₁-14 _(n) respectively generate sense signals I_(FB1)-I_(FBn), which respectively represent the phase currents i₁-i_(n). For example, each of the signals I_(FB1)-I_(FBn) may be a respective voltage that has substantially the same signal phase as the corresponding phase current i and that has an amplitude that is substantially proportional to the amplitude of the corresponding phase current.

In addition to the current sensors 14 ₁-14 _(n), the converter 10 includes a coupled-inductor assembly 16 having windings 18 ₁-18 _(n), which are wound about a common core (not shown in FIG. 1) and which are magnetically coupled to one another via the core, a power-supply controller 20, high-side drive transistors 22 ₁-22 _(n), low-side drive transistors 24 ₁-24 _(n), a filter capacitor 26, and an optional filter inductor 28. A winding 18 and the high-side and low-side transistors 22 and 24 coupled to the winding at a phase intermediate node INT compose a respective phase 12. For example, the winding 18 ₁ and the transistors 22 ₁ and 24 ₁ compose the phase 12 ₁.

The controller 20 may be any type of controller suitable for use in a multiphase CI power supply, is supplied by voltages VDD_(controller) and VSS_(controller), and receives the regulated output voltage V_(out), a reference voltage V_(ref), and the sense signals I_(FB1)-I_(FBn), which are fed back to the controller from the current sensors 14 ₁-14 _(n), respectively. The controller 20 may use V_(ref) and the fed back V_(out) and I_(FB1)-I_(FBn) to conventionally regulate V_(out) to a desired value.

The high-side transistors 22 ₁-22 _(n), which are each switched “on” and “off” by the controller 20, are power NMOS transistors that are respectively coupled between input voltages VIN₁-VIN_(n) and the nodes INT₁-INT_(n). Alternatively, the transistors 22 ₁-22 _(n) may be other than power NMOS transistors, and may be coupled to a common input voltage. Moreover, the transistors 22 ₁-22 _(n) may be integrated on the same die as the controller 20, may be integrated on a same die that is separate from the die on which the controller is integrated, or may be discrete components.

Similarly, the low-side transistors 24 ₁-24 _(n), which are each switched on and off by the controller 20, are power NMOS transistors that are respectively coupled between low-side voltages VL₁-VL_(n) and the nodes INT₁-INT_(n) of the phase windings 18 ₁-18 _(n). Alternatively, the transistors 24 ₁-24 _(n) may be other than power NMOS transistors, and may be coupled to a common low-side voltage such as ground. Moreover, the transistors 24 ₁-24 _(n) may be integrated on the same die as the controller 20, may be integrated on a same die that is separate from the die on which the controller is integrated, may be integrated on a same die as the high-side transistors 22 ₁-22 _(n), may be integrated on respective dies with the corresponding high-side transistors 22 ₁-22 _(n) (e.g., transistors 22 ₁ and 24 ₁ on a first die, transistors 22 ₂ and 24 ₂ on a second die, and so on), or may be discrete components.

The filter capacitor 26 is coupled between the regulated output voltage V_(out) and a voltage VSS_(cap), and works in concert with the windings 18 ₁-18 _(n) and an optional filter inductor 28 (if present) to maintain the amplitude of the steady-state ripple-voltage component of V_(out) within a desired range which may be on the order of hundreds of microvolts (μV) to tens of millivolts (mV). Although only one filter capacitor 26 is shown, the converter 10 may include multiple filter capacitors coupled in electrical parallel. Furthermore, VSS_(cap) may be equal to VSS_(controller) and to VL₁-VL_(n); for example, all of these voltages may equal ground.

As further discussed below, the filter inductor 28 may be omitted if the leakage inductances L_(lk1)-L_(lkn) (discussed below) of the windings 18 ₁-18 _(n) are sufficient to perform the desired inductive filtering function. In some applications, the filter inductor 28 may be omitted to reduce the size and component count of the converter 10.

Each of the windings 18 ₁-18 _(n) of the coupled-inductor assembly 16 may be modeled as a self inductance L and a resistance DCR. For purposes of discussion, only the model components of the winding 18 ₁ are discussed, it being understood that the model components of the other windings 18 ₂-18 _(n) are similar, except for possibly their values.

The self inductance L₁ of the winding 18 ₁ may be modeled as two zero-resistance inductances: a magnetic-coupling inductance L_(C1), and a leakage inductance L_(lk1). When a phase current i₁ flows through the winding 18 ₁, the current generates a magnetic flux. The value of the coupling inductance L_(C1) is proportional to the amount of this flux that is coupled to other windings 18 ₂-18 _(n), and the value of the leakage inductance L_(lk1) is proportional to the amount of the remaining flux, which is not coupled to the other windings 18 ₂-18 _(n). In one embodiment, L_(C1)=L_(C2)= . . . =L_(Cn), and L_(lk1)=L_(lk2)= . . . =L_(lkn), although inequality among the coupling inductances L_(C), the leakage inductances L_(lk), or both L_(C) and L_(lk), is contemplated. Furthermore, in an embodiment, the respective magnetic-coupling coefficients between pairs of coupling inductances L_(c) are equal (i.e., a current through L_(C1) magnetically induces respective equal currents in L_(C2), . . . L_(Cn)), although unequal coupling coefficients are contemplated.

The resistance DCR₁ is the resistance of the winding 18 ₁ when a constant voltage V₁ is applied across the winding and causes a constant current I₁ to flow through the winding. That is, DCR₁=V₁/I₁.

The power supply 10 may provide the regulated voltage V_(out) to a load 30, such as a microprocessor.

Still referring to FIG. 1, alternate embodiments of the power supply 10 are contemplated. Some or all of the phases 12 ₁-12 _(n) may be magnetically uncoupled from one another. For example, phases 12 ₁ and 12 ₂ may be formed on a first core and thus may be magnetically coupled, and phases 12 ₃ and 12 ₄ may be formed on a second core separate from the first core, and thus may be magnetically coupled to one another but magnetically uncoupled form the phases 12 ₁ and 12 ₂. Or, a phase 12 may be magnetically uncoupled from all other phases 12. Furthermore, although described as a multiphase buck converter, the power supply 10 may be any other type of multiphase power supply.

FIG. 2 is a schematic diagram of a portion of the power supply 10 of FIG. 1 including the windings 18 ₁-18 _(n) and an embodiment of the current sensors 14 ₁-14 _(n). For purposes of discussion, it is assumed that all of the windings 18 ₁ and 18 _(n) are magnetically coupled to one another, and that the filter inductor 28 is omitted from the supply 10. For brevity, only the sensor 14 ₁ is discussed, it being understood that the other sensors 14 are similar except for possibly the values of the components that compose the other sensors.

The sensor 14 ₁ includes a capacitor C₁ across which the sense signal I_(FB1) (here a voltage signal) is generated, an optional scaling resistor RC₁ coupled across C₁, and resistors R₁₁-R_(n1), which are respectively coupled between the nodes INT₁-INT_(n) and C₁.

The resistor R₁₁ couples to C₁ a signal (a current in this embodiment) that represents the portion of the phase current i₁ that the switching transistors 22 ₁ and 24 ₁ (FIG. 1) cause to flow through the winding 18 ₁.

And the resistors R₂₁-R_(n1) each couple to C₁ a respective signal (a current in this embodiment) that represents the respective portion of i₁ that a respective phase current i₂-i_(n) magnetically induces in the winding 18 ₁. That is, the resistor R₂₁ couples to C₁ a current that is proportional to the portion of i₁ that the phase current i₂ magnetically induces in the winding 18 ₁. Similarly, the resistor R₃₁ couples to C₁ a current that is proportional to the portion of i₁ that the phase current_(i3) magnetically induces in the winding 18 ₁, and so on.

C₁ generates from the sum of the signals from R₁₁-R_(n1) the sense voltage I_(FB1), which has the same phase as i₁ and which has an amplitude that is proportional to the amplitude of i₁.

Therefore, a power-supply controller, such as the controller 20 of FIG. 1, may obtain from I_(FB1) an accurate representation of the instantaneous phase and amplitude of the phase current i₁.

In a similar manner, the capacitors C₂-C_(n) respectively generate the sense voltages I_(FB2)-I_(FBn), from which a power-supply controller, such as the controller 20 of FIG. 1, may obtain accurate representations of the instantaneous phases and amplitudes of the phase currents i₂-i_(n).

FIG. 3 is a schematic diagram of a two-phase (n=2) version of the power-supply portion of FIG. 2.

Referring to FIG. 3, an embodiment of a technique for calculating values for R₁₁, R₁₂, R₂₁, R₂₂, C₁, and RC₁ (if present) is presented. To simplify the presentation, it is assumed that R₁₁=R₂₂=R₁, R₂₁=R₁₂=R₂, L_(C1)=L_(C2)=L_(C), L_(Llk1)=L_(lk2)=L_(lk), DCR₁=DCR₂=DCR, and RC₁=RC₂=∞ (i.e., RC₁ and RC₂ are omitted) in equations (1)-(16) below. It is, however, understood that the disclosed embodiment may be extrapolated to a more general embodiment of FIGS. 2-3 for R₁₁≠R₂₂, R₂₁≠R₁₂, L_(C1)≠L_(C2), L_(lk1)≠L_(lk2), DCR₁≠DCR₂, RC₁≠RC₂≠∞, and n>2.

Still referring to FIG. 3, the following equations are derived from the general relationship between the currents through and the voltages across reverse-coupled inductors-the windings 18 ₁ and 18 ₂ are reversed coupled when a positive current flowing through the winding 18 ₁ into the node 11 induces a positive current in the winding 18 ₂ also flowing into the node 11. V ₁ =s·(L _(lk) +L _(C))·i ₁ −s·L _(C) ·i ₂ +DCR·i ₁   (1) V ₂ =s·(L _(lk) +L _(C))·i ₂ −s·L _(C) ·i ₁ +DCR·i ₂ and   (2)

$\begin{matrix} {i_{2} = \frac{V_{2} + {s \cdot {Lc} \cdot i_{1}}}{{s \cdot \left( {L_{lk} + L_{C}} \right)} + {DCR}}} & (3) \end{matrix}$ where V₁ and V₂ are the voltages at nodes INT₁ and INT₂, respectively.

From equations (1)-(3), one may derive the following equation for i₁:

$\begin{matrix} {i_{1} = \frac{{V_{1} \cdot \left\lbrack {{s \cdot \left( {L_{lk} + L_{C}} \right)} + {DCR}} \right\rbrack} + {s \cdot L_{C} \cdot V_{2}}}{\left\lbrack {{s\left( {L_{lk} + L_{C}} \right)} + {DCR}} \right\rbrack^{2} - \left\lbrack {s \cdot L_{C}} \right\rbrack^{2}}} & (4) \end{matrix}$

Furthermore, where R₁₁=R₁ and R₂₁=R₂ are the resistors coupled to the capacitor C₁, one may derive the following equation for the voltage I_(FB1) across C₁:

$\begin{matrix} {I_{{FB}\; 1} = {{\frac{\frac{R_{1}}{1 + {s \cdot R_{1} \cdot C_{1}}}}{\frac{R_{1}}{1 + {s \cdot R_{1} \cdot C_{1}}} + R_{2}} \cdot V_{1}} + {\frac{\frac{R_{2}}{1 + {s \cdot R_{2} \cdot C_{1}}}}{\frac{R_{2}}{1 + {s \cdot R_{2} \cdot C}} + R_{1}} \cdot V_{2}}}} & (5) \end{matrix}$

Because the voltage VDCR₁ across DCR₁ equals i₁·DCR₁, VDCR₁ has the same phase as i₁, and has an amplitude that is proportional (by a factor DCR₁) to the amplitude of i₁; as discussed above in conjunction with FIG. 1, these attributes are suitable for I_(FB1).

Unfortunately, DCR₁ is a modeled component, and one does not have physical access to the voltage VDCR₁ across it.

But, one can set I_(FB1)=VDCR₁=i₁·DCR₁ according to the following equation, which is derived from equations (4) and (5):

$\begin{matrix} {\frac{{R_{1} \cdot V_{1}} + {R_{2} \cdot V_{2}}}{R_{1} + R_{2} + {s \cdot R_{1} \cdot R_{2} \cdot C_{1}}} = {\frac{{V_{1} \cdot \left\lbrack {{s \cdot \left( {L_{lk} + L_{C}} \right)} + {DCR}} \right\rbrack} + {s \cdot L_{C} \cdot V_{2}}}{\left\lbrack {{s\left( {L_{lk} + L_{C}} \right)} + {s \cdot L_{C}} + {DCR}} \right\rbrack \cdot \left\lbrack {{s \cdot L_{lk}} + {DCR}} \right\rbrack} \cdot {DCR}}} & (6) \end{matrix}$

From equation (6), one can derive the following two equations:

$\begin{matrix} {\frac{R_{1} \cdot V_{1}}{R_{1} + R_{2} + {s \cdot R_{1} \cdot R_{2} \cdot C_{1}}} = {\frac{V_{1} \cdot \left\lbrack {{s \cdot \left( {L_{lk} + L_{C}} \right)} + {DCR}} \right\rbrack}{\left\lbrack {{s\left( {L_{lk} + L_{C}} \right)} + {s \cdot L_{C}} + {DCR}} \right\rbrack \cdot \left\lbrack {{s \cdot L_{lk}} + {DCR}} \right\rbrack} \cdot {DCR}}} & (7) \\ {\frac{R_{2} \cdot V_{2}}{R_{1} + R_{2} + {s \cdot R_{1} \cdot R_{2} \cdot C_{1}}} = {\frac{s \cdot L_{C} \cdot V_{2}}{\left\lbrack {{s\left( {L_{lk} + L_{C}} \right)} + {s \cdot L_{C}} + {DCR}} \right\rbrack \cdot \left\lbrack {{s \cdot L_{lk}} + {DCR}} \right\rbrack} \cdot {DCR}}} & (8) \end{matrix}$

Referring to FIG. 1, if one assumes that the controller 20 switches the transistors 22 and 24 at a relatively high frequency, e.g., 100 KHz or higher (this assumption applies in many applications of multiphase power supplies), then one may assume that s(L_(lk)+L_(c)) and sL_(ik) are much greater than DCR. Applying these assumptions, equations (7) and (8) respectively reduce to the following equations:

$\begin{matrix} {\frac{R_{1} \cdot \left( {1 + {s \cdot \frac{L_{lk}}{DCR}}} \right)}{\left( {R_{1} + R_{2}} \right) \cdot \left( {1 + {s \cdot \frac{R_{1} \cdot R_{2}}{R_{1} + R_{2}} \cdot C}} \right)} = \frac{L_{lk} + L_{C}}{L_{lk} + {2L_{C}}}} & (9) \\ {\frac{R_{2} \cdot \left( {1 + {s \cdot \frac{L_{lk}}{DCR}}} \right)}{\left( {R_{1} + R_{2}} \right) \cdot \left( {1 + {s \cdot \frac{R_{1} \cdot R_{2}}{R_{1} + R_{2}} \cdot C}} \right)} = \frac{L_{C}}{L_{lk} + {2L_{C}}}} & (10) \end{matrix}$

From equations (9) and (10), one may derive the following design equations for the sensor circuit 14 ₁ of FIG. 3:

$\begin{matrix} {\frac{R_{1}}{R_{1} + R_{2}} = \frac{L_{lk} + L_{C}}{L_{lk} + {2L_{C}}}} & (11) \\ {\frac{R_{2}}{R_{1} + R_{2}} = \frac{L_{C}}{L_{lk} + {2L_{C}}}} & (12) \\ {\frac{L_{lk}}{DCR} = {\frac{R_{1} \cdot R_{2}}{R_{1} + R_{2}} \cdot C_{1}}} & (13) \end{matrix}$

Therefore, by selecting the components R₁₁=R₁, R₂₁=R₂, and C₁ (L_(C1)=L_(C), L_(lk1)=L_(lk), and DCR₁=DCR are assumed to be known quantities for purposes of this disclosure) of the sensor circuit 14 ₁ such that they satisfy the design equations (11)-(13), the results are that I_(FB1)≈i₁·DCR₁, and therefore, that I_(FB1) has approximately the same phase as i₁, and has an amplitude that is approximately proportional to (i.e., that has approximately the same amplitude profile as) the amplitude of i₁. Furthermore, because at least in some applications the design equation (12) may be redundant, one may design the sensor circuit 14 ₁ by selection component values that satisfy only the equations (11) and (13).

FIGS. 4A-4D are respective timing diagrams of I_(FB1), i₁, I_(FB2), and i₂ of FIG. 3 for a two phase embodiment of the power-supply 10 of FIG. 1 for the following component values, which satisfy the design equations (11)-(13): L_(lk1)=L_(lk2) =200 nanohenries (nH), L_(c1)=L_(c2) =500 nH, DCR₁=DCR₂ =2 milliohms (mΩ), C₁ =₂=0.01 microfarads (μF), R₁₁=R₂₂=17 kiloohms (KΩ), and R₁₂=R₂₁=24 KΩ. Although I_(FB1) and I_(FB2) are voltages, the timing diagrams of FIGS. 4A and 4C are in units of Amperes (current) because I_(FB1) and I_(FB2) respectively represent the phase currents i_(i) and i₂. For purposes of plotting only, I_(FB1) and I_(FB2) have been normalized by setting DCR₁=DCR₂=1 such that I_(FB1) has the same amplitude profile and phase as i₁, and I_(FB2) has the same amplitude profile and phase as i₂. Of course the power-supply controller 20 (FIG. 1) may adjust the amplitude of the I_(FB1) and I_(FB2) within the controller by a scale factor other than unity.

Referring again to FIGS. 1-4D, alternate embodiments of the disclosed technique for designing the sensor circuits 14 ₁-14 _(n) are contemplated. For example, equations (1)-(13) may be extrapolated for the design of the power supply 10 having more than n=2 magnetically coupled phases 12 ₁ and 12 ₂ (i.e., for n>2). But the equations (1)-(13) may also be suitable for an embodiment of the power supply 10 having only pairs of magnetically coupled phases 12, e.g., phase 12 ₁ coupled to phase 12 ₂ only, phase 12 ₃ coupled to phase 12 ₄ only, and so on. Furthermore, one may modify the equations (1)-(13) to cover an embodiment of the power supply 10 where one or more components of the sensor circuit 14 and winding 18 of one phase 12 have different values than the corresponding one or more components of the sensor circuit 14 and winding 8 of another phase 12. Moreover, one may modify equations (9)-(13) so that they are not simplified based on the assumption that the controller 20 switches the phases 12 at a relatively high frequency. In addition, although the sensor circuits 14 are described as being useful to sense the currents through magnetically coupled phases 12, one may use the sensor circuits 14 or similar sensor circuits to sense the currents through magnetically uncoupled phases. Furthermore, the disclosed technique, or a modified version thereof, may be suitable for designing the sensor circuits of a multiphase power supply other than a buck converter. Moreover, although an embodiment of a technique for designing the sensor circuit 14, is disclosed the same or a similar embodiment may be used to design the sensor circuit 14 ₂. In addition, although the sensor circuits 14 ₁-14 _(n) are disclosed as each being coupled to the intermediate nodes INT₁-INT₂, the sensor circuits may be coupled to other non-output nodes of phases 12 ₁-12 _(n). The output node of a phase 12 is the node where all of the phases are coupled together, for example the node 11 in FIG. 2 where the filter inductor 28 is omitted.

Referring again to FIG. 3, one may wish to include the optional resistor RC₁ in the sensor circuit 14 ₁ to scale the voltage I_(FB1) such that K₁·I_(FB1)=i₁·DCR₁, and thus I_(FB1)=(i₁·DCR₁)/K₁, where K₁≦1 (K₁=1 when RC₁ is omitted). When RC₁ is present and n=n, then the design equations (11) and (13) may be respectively modified into the following equations, assuming that the values of L_(C), L_(lk), and DCR are the same for each winding 18 ₁-18 _(n)(because the design equation (12) may redundant as discussed above, the equation into which one may modify equation (12) when RC₁ is present is omitted for brevity):

$\begin{matrix} {\frac{R_{11}}{R_{11} + R_{21} + \ldots + R_{n\; 1}} = \frac{L_{lk} + L_{C}}{L_{lk} + {nL}_{C}}} & (14) \\ {\frac{L_{lk}}{DCR} = {\frac{R_{11} \cdot R_{21} \cdot \ldots \cdot R_{n\; 1} \cdot {RC}_{1}}{R_{11} + R_{21} + \ldots + R_{n\; 1}} \cdot C_{1}}} & (15) \end{matrix}$

And K₁ is given by the following equation:

$\begin{matrix} {K_{1} = \frac{\left( {R_{11} + R_{21} + \ldots + R_{n\; 1}} \right) \cdot {RC}_{1}}{{\left( {R_{11} + R_{21} + \ldots + R_{n\; 1}} \right) \cdot {RC}_{1 +}}{R_{11} \cdot R_{21} \cdot \ldots \cdot R_{n\; 1}}}} & (16) \end{matrix}$

The modified design equations for the components of the sensor circuits 14 ₂-14 _(n) and the equations for the scale factors K₂-K_(n) may be respectively similar to equations (14)-(16). Furthermore, equations (14)-(16) may be modified where L_(C), L_(lk), and DCR are not the same for each winding 18 ₁-18 _(n).

FIG. 5 is schematic diagram of a portion of a two-phase (n=2) version of the power supply 10 of FIG. 1 including the windings 18 ₁ and 18 ₂ (which we magnetically coupled) and another embodiment of the sensor circuits 14 ₁ and 14 ₂. For purposes of discussion, it is assumed that the filter inductor 28 is omitted from the power supply 10. For brevity, only the sensor circuit 14 ₁ is discussed, it being understood that the other sensor circuit 14 ₂ is similar except for possibly the values of the components that compose the sensor circuit 14 ₂.

The sensor 14 ₁ includes a capacitor C₁ across which the sense signal I_(FB1) (here a voltage signal) is generated, an optional scaling resistor RC₁ across the capacitor C₁, a resistor R₁ coupled to the capacitor C₁, and a resistor R₁₁, which is coupled between the phase intermediate node INT₁ and the resistor R₁. The resistors R₁₁ and R₁ couple to C₁ a signal (a current in this embodiment) that represents the portion of the phase current i₁ that the switching transistors 22 ₁ and 24 ₁ (FIG. 1) cause to flow through the winding 18 ₁.

Similarly, the sensor circuit 14 ₂ includes a capacitor C₂ across which the sense signal I_(FB2) (here a voltage signal) is generated, an optional scaling resistor RC₂ across the capacitor C₂, a resistor R₂ coupled to the capacitor C₂, and a resistor R₂₂, which is coupled between the phase intermediate node INT₂ and the resistor R₂. The resistors R₂₂ and R₂ couple to C₂ a signal (a current in this embodiment) that represents the portion of the phase current i₂ that the switching transistors 22 ₂ and 24 ₂ (FIG. 1) cause to flow through the winding 18 ₂.

The sensor circuits 14 ₁ and 14 ₂ also “share” a resistor R₁₂, which is coupled between the resistors R₁ and R₂ and also between the resistors R₁₁ and R₂₂. The resistors R₂₂, R₁₂, and R₁ couple to C₁ a signal (a current in this embodiment) that represents the portion of the phase current i₁ that the phase current i₂ magnetically induces in the winding 18 ₁. That is, the resistors R₂₂, R₁₂, and R₁ couple to C₁ a current that is proportional to the portion of i₁ that i₂ magnetically induces in the winding 18 ₁. Similarly, the resistors R₁₁, R₁₂, and R₂ couple to C₂ a signal (a current in this embodiment) that represents the portion of the phase current i₂ that the phase current i₁ magnetically induces in the winding 18 ₂.

One may extrapolate the sensor circuit 14 ₁ for use in the power supply 10 (FIG. 1) where n>2 by including in the sensor circuit a respective resistive network between the node INT₁ and all the other nodes INT₂-INT_(n), where each resistive network may be similar to the network of resistors R₁₁, R₁₂, and R₂₂, except possibly for the values of these resistors. The resistor R₁ would be coupled to the respective nodes of these resistive networks corresponding the node between R₁₁ and R₂₂ in FIG. 5. And the resistors corresponding to the resistor R₂ in FIG. 5 would be respectively coupled to the nodes corresponding to the node between R₁₂ and R₂₂ in FIG. 5.

One may extrapolate the sensor circuit 14 ₂ for use in the power supply 10 (FIG. 1) where n>2 in a similar manner, and the sensor circuits 14 ₃-14 _(n) may each be similar to the sensor circuits 14 ₁ and 14 ₂, except possibly for the values of the resistors.

Still referring to FIG. 5, in an embodiment one may derive design equations for the sensor circuit 14 ₁ in a manner similar to that presented above in conjunction with FIG. 3. Assuming an embodiment of the sensor circuit 14 ₁ where L_(c1)=L_(c2)=L_(c), L_(lk1)=L_(lk2)=L_(lk), DCR₁=DCR₂=DCR, R₁₁=R₂₂=R_(A), and R₁₂=R_(B), the design equations for such an embodiment are as follows:

$\begin{matrix} {\frac{R_{A}}{R_{A} + R_{B}} = \frac{L_{C}}{L_{lk} + {2L_{C}}}} & (17) \\ {\frac{L_{lk}}{DCR} = {R_{1} \cdot C}} & (18) \\ {K_{1} = \frac{{RC}_{1}}{R_{1} + {RC}_{1}}} & (19) \end{matrix}$

Referring again to FIGS. 1 and 5, alternate embodiments of the disclosed technique for designing the sensor circuits 14 ₁-14 _(n) of FIG. 5 are contemplated. For example, equations (17)-(19) may be modified for the design of the power supply 10 having more than n=2 magnetically coupled phases 12 ₁ and 12 ₂ (i.e., for n>2). But the equations (17)-(19) may also be suitable for an embodiment of the power supply 10 having only pairs of magnetically coupled phases 12, e.g., phase 12 ₁ coupled to phase 12 ₂ only, phase 12 ₃ coupled to phase 12 ₄ only, and so on. Furthermore, one may modify the equations (17)-(19) to cover an embodiment of the power supply 10 where one or more components of the sensor circuit 14 and winding 18 of one phase 12 have different values than the corresponding one or more components of the sensor circuit 14 and winding 18 of another phase 12. Moreover, one may modify equations (17)-(19) so that they are not simplified based on the assumption that the controller 20 switches the phases 12 at a relatively high frequency. In addition, although the sensor circuits 14 of FIG. 5 are described as being useful to sense the currents through magnetically coupled phases 12, one may use the sensor circuits 14 or similar sensor circuits to sense the currents through magnetically uncoupled phases. Furthermore, the disclosed technique, or a modified version thereof, may be suitable for designing the sensor circuits of a multiphase power supply other than a buck converter. Moreover, although an embodiment of a technique for designing the sensor circuit 14, is disclosed, the same or a similar embodiment may be used to design the sensor circuit 142. In addition, although the sensor circuits 14 ₁-14 ₂ are disclosed as each being coupled to the intermediate nodes INT₁-INT₂, the sensor circuits 14 ₁-14 ₂ (and 14 ₃-14 _(n) of present) may be coupled to other non-output nodes of the phases 12 ₁-12 ₂ (and 12 ₃-12 _(n) of present).

FIG. 6 is a block diagram of an embodiment of a system 40 (here a computer system), which may incorporate a multiphase power supply 42 (such as the multiphase power supply 10 of FIG. 1) that includes one or more phase-current sensor circuits that are the same as or that are similar to embodiments of one or more of the current sensor circuits 14 of FIGS. 2, 3, and 5.

The system 40 includes computer circuitry 44 for performing computer functions, such as executing software to perform desired calculations and tasks. The circuitry 44 typically includes a controller, processor, or one or more other integrated circuits (ICs) 46, and the power supply 42, which provides power to the IC(s) 46—these IC(s) compose(s) the load of the power supply. The power supply 42, or a portion thereof, may be disposed on the same IC die as one or more of the ICs 46, or may be disposed on a different IC die.

One or more input devices 48, such as a keyboard or a mouse, are coupled to the computer circuitry 44 and allow an operator (not shown) to manually input data thereto.

One or more output devices 100 are coupled to the computer circuitry 44 to provide to the operator data generated by the computer circuitry. Examples of such output devices 50 include a printer and a video display unit.

One or more data-storage devices 52 are coupled to the computer circuitry 44 to store data on or retrieve data from external storage media (not shown). Examples of the storage devices 52 and the corresponding storage media include drives that accept hard and floppy disks, tape cassettes, compact disk read-only memories (CD-ROMs), and digital-versatile disks (DVDs).

From the foregoing it will be appreciated that, although specific embodiments have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of this disclosure. Furthermore, where an alternative is disclosed for a particular embodiment, this alternative may also apply to other embodiments even if not specifically stated. 

What is claimed is:
 1. A power supply, comprising: a supply output node configured to carry a regulated output voltage; phase paths each having a respective phase-path output node coupled to the supply output node, each having a respective phase-path non-output node, and each configured to carry a respective phase current, at least two of the phase paths magnetically coupled to one another; and at least two sensor circuits each having a respective first sensor node coupled to the phase-path non-output nodes of the at least two phase paths and each configured to generate a respective sense signal that represents the phase current flowing through a respective one of the at least two phase paths.
 2. The power supply of claim 1 wherein all of the phase paths are magnetically coupled to one another.
 3. The power supply of claim 1 wherein: the phase paths each include a respective inductor coupled between the phase-path non-output node and the output node; and wherein the inductors of each of the at least two phase paths are magnetically coupled to one another.
 4. The power supply of claim 1 wherein each of the at least two sensor circuits is configurable to generate as the respective sense signal a respective voltage that represents an amplitude and a phase of the phase current flowing through a respective one of the at least two phase paths.
 5. The power supply of claim 1 wherein each of the at least two sensor circuits: includes a respective second sensor node coupled to the supply output node; and is configured to generate as the respective sense signal a respective voltage between the first and second sensor nodes.
 6. The power supply of claim 1 wherein each of the at least two sensor circuits includes: a respective second sensor node coupled to the supply output node; and a respective component coupled between the first and second sensor nodes.
 7. The power supply of claim 1 wherein each of the at least two sensor circuits includes: a respective second sensor node coupled to the supply output node; and a respective capacitor coupled between the first and second sensor nodes.
 8. The power supply of claim 1 wherein each of the at least two sensor circuits includes: a respective second sensor node coupled to the supply output node; and a respective capacitor and a respective resistor coupled in parallel between the first and second sensor nodes.
 9. The power supply of claim 1 wherein each of the at least two sensor circuits includes: a respective second sensor node coupled to the supply output node; a respective first resistor coupled to the first sensor node; a respective capacitor and a respective second resistor coupled in parallel between the first resistor and the second sensor node; and respective third resistors each coupled between the first resistor and a phase-path non-output node of a respective one of the at least two phase paths.
 10. The power supply of claim 1 wherein each of the at least two sensor circuits further includes components each coupled between the first sensor node and a phase-path non-output node of a respective one of the at least two phase paths.
 11. The power supply of claim 1 wherein each of the at least two sensor circuits further includes respective resistors each coupled between the respective first sensor node and a phase-path non-output node of a respective one of the at least two phase paths.
 12. The power supply of claim 1, further comprising resistors each coupled between respective pairs of the first sensor nodes of the at least two phase paths.
 13. The power supply of claim 1 wherein at least one of the phase paths has a respective phase-path non-output node, has a respective phase-path output node coupled to the supply output node, and is configured to carry a respective phase current, the at least one phase path being magnetically uncoupled from the other phase paths.
 14. The power supply of claim 1, further comprising: phase-path drivers each coupled to a phase-path non-output node of a respective one of the phase paths; and a controller coupled to the at least two sensor circuits and the phase-path drivers and configured to regulate the output voltage by controlling the phase-path drivers coupled to the at least two phase paths in response to the sense signals.
 15. The power supply of claim 1, further comprising: phase-path drivers each coupled to a phase-path non-output node of a respective one of the phase paths; and a controller coupled to the supply output node, the at least two sensor circuits, and the phase-path drivers and configured to regulate the output voltage by controlling the phase-path drivers coupled to the at least two phase paths in response to the output voltage and the sense signals.
 16. The power supply of claim 1, further comprising: wherein each of the at least two sensor circuits includes a respective second sensor node; and a filter coupled between the second sensor nodes of the at least two sensor circuits and the supply output node.
 17. The power supply of claim 1, further comprising: a reference node; wherein each of the at least two sensor circuits includes a respective second sensor node; a filter inductor coupled between the second sensor nodes of the at least two sensor circuits and the supply output node; and a filter capacitor coupled between the reference node and the supply output node.
 18. The power supply of claim 1, further comprising: a reference node; wherein each of the at least two sensor circuits includes a respective second sensor node coupled to the supply output node; and a filter capacitor coupled between the reference node and the supply output node.
 19. A system, comprising: a power supply, including a supply output node configured to carry a regulated output voltage, phase paths each having a respective phase-path non-output node, each having a respective phase-path output node coupled to the supply output node, and each configured to carry a respective phase current, at least two of the phase paths magnetically coupled to one another, at least two sensor circuits each having a respective first sensor node coupled to the phase-path non-output nodes of the at least two phase paths and each configured to generate a respective sense signal that represents the phase current flowing through a respective one of the at least two phase paths, phase-path drivers each coupled to a phase-path non-output node of a respective one of the phase paths, and a power-supply controller coupled to the sensor circuits and the phase-path drivers and configurable to regulate the output voltage by controlling the phase-path drivers coupled to the at least two phase paths in response to the sense signals; and a load coupled to the supply output node of the power supply.
 20. The system of claim 19 wherein: the power-supply controller is disposed on a first integrated-circuit die; and the load is disposed on a second integrated-circuit die.
 21. The system of claim 19 wherein: the power-supply controller is disposed on an integrated-circuit die; and the load is disposed on the same integrated-circuit die.
 22. The system of claim 19 wherein the load includes an integrated circuit.
 23. A method, comprising: driving first and second power-supply phase paths with respective first and second driving signals to generate an output voltage; generating in response to the first and second driving signals a first sense signal that represents a first phase-path current flowing through the first power-supply phase path; and regulating the output voltage in response to the first sense signal.
 24. The method of claim 23, further comprising magnetically coupling the first power-supply phase path to the second power-supply phase path.
 25. The method of claim 23 wherein generating the first sense signal includes generating the first sense signal across a first impedance by coupling the first and second drive signals to the first impedance via respective second impedances.
 26. The method of claim 23 wherein generating the first sense signal includes generating the first sense signal substantially equal to a first voltage across a capacitor by coupling the first and second drive signals to the capacitor via respective resistors.
 27. The method of claim 23 wherein generating the first sense signal includes generating the first sense signal substantially equal to a first voltage across a parallel combination of a first resistor and a capacitor by coupling the first and second drive signals to the parallel combination via respective second resistors.
 28. The method of claim 23, further comprising: generating in response to the first and second driving signals a second sense signal that represents a second phase-path current flowing through the second power-supply phase path; and wherein regulating the output voltage includes regulating the output voltage in response to the first and second sense signals.
 29. The method of claim 23, further comprising: driving a third power-supply phase path with a third driving signal to generate the output voltage; wherein generating the first sense signal includes generating the first sense signal in response to the first, second, and third driving signals; generating in response to the first, second, and third driving signals second and third sense signals that respectively represent second and third phase-path currents flowing through the second and third power-supply phase paths; and regulating the output voltage in response to the first, second, and third sense signals. 